Patent GB-1207597-A (GB)
Title: Method of and apparatus for generating an electrical voltage corresponding to a contour profile curve of a surface to be tested for coarseness
Inventor: PERTHEN JOHANNES
IPC: G01B7/34
Filed: 1968-03-28
Abstract: 1,207,597. Measuring profiles electrically. J. PERTHEN. March 28, 1968 [Oct. 27, 1967], No.14909/68. Heading G1N. The contour profile of surface roughness is produced by moving an electro-mechanical tracer linearly over a surface firstly in one direction and then in the reverse direction, converting the actual output voltage profile U produced into a series of arcuate curves U3V, U3R, Figs.3 and 4, each commencing at a voltage peak and decreasing until the flank of an adjacent peak is encountered, recording the arcuate voltage curves U3V, Fig. 3, produced by tracer movement in the first direction, and comparing them at each instant until the arcuate voltage curves U3R, Fig. 4, produced during the return movement, the higher up the compared voltages at each instant defining the contour profile U3, Fig. 1. The contour profile thus obtained is equivalent to the path of the centre of a ball rolled over the surface under investigation. In one arrangement the output from a roughness tracer 1, Fig.2, e.g. the voltage across the diagonal of an A. C. inductive bridge, is fed via amplifier 7, demodulator 8 and diode 2 to capacitor C1, connected in series with resistor R3, parallel-connected resistor R1 being provided through which the capacitor C2 discharges. The junction between resistor R1 and capacitor C1 is connected to the base of a transistor Tr which conducts while capacitor C1 charges and becomes non-conductive when charging ceases, i.e. when the tracer passes over a roughness peak. Capacitor C2 connected across the transistor discharges while capacitor C1 is being charged, and is charged by capacitor C1 when charging of this condenser ceases, the voltage across resistor R2 being indicative of the charge on capacitor C1. This voltage is recorded on a tape 12 driven by a motor 4 synchronously with the tracer head. At the end of the forward motion the movements are reversed by a relay Rel, the voltage across resistor R2 being supplied to a diode D2. Simultaneously the voltage recorded on tape 12 is read out and fed to a diode D3 which is so connected with diode D2 that only the larger of the two signals at each instant is transmitted to a differential amplifier 18. This signal has the form of the contour profile U3. The signal across a potential divider R4, R5, indicative of the actual surface roughness, is also fed to the differential amplifier, the amplifier output being integrated at 22 to provide a measure of the smoothing depth Rp, Fig. 1, of the surface. Alternatively the output from the differential amplifier may be fed to a peak-voltage measuring instrument to indicate peak-to-valley depth of the surface. For computing the average and r.m.s. height of the surface both signals U3V and U3R are recorded and the value of Rp compared and stored. The signal U3 is then computed, reduced according to Rp, and integrated to produce the average and r.m.s. heights of the surface. In an alternative embodiment, Fig. 7, the output from the demodulator is connected across a resistor R9 and series capacitor C1 to charge the capacitor. The junction between the resistor and capacitor is connected to the base of transistor T20 which is rendered conductive when the capacitor is being charged and so disables a transistor T10. When capacitor charging ceases at a surface peak, transistor T20 is blocked and a capacitor C4 is then charged from a D.C. source UK to affect the degree of conductivity of transistor T10. The output voltage then drops from the peak voltage on capacitor C1 as this condenser is discharged through the transistor until recharging recommences.